Ambient temperature compensating bimetal mechanisms have been known heretofore. However, in such prior thermal mechanisms, it has been the practice generally to use bimetal deflection with temperature to perform work. In such mechanisms, the high work demand occurs when the bimetal is hot and is weakest metallurgically, thereby involving physical damage to the bimetal due to the danger of over-stress. While these prior bimetal mechanisms have been useful for their intended purposes, they have nevertheless been handicapped by the fact that the highest work demand occurs when the bimetal is the hottest and structurally the weakest with its consequent susceptibility to over-stress and possible structural damage. It has, therefore, been found desirable to provide an improve bimetal mechanism wherein the electrically heated bimetal member that senses an overload condition or the like merely triggers or permits the unlatching function to take place while the actual work is performed by other means.